Water displacement and water friction of marine vessels accounts for some of the biggest costs and power uses required to drive a vessel through water. Various strategies to reduce water displacement have included planning surface areas and V-shaped hulls. One of the first improvements over displacement hulls is the design of planing hulls. Planing hulls work well for light weight crafts in smooth water or water with very small waves. Most planing hulls are designed to plane at cruising speeds. If the water waves are large the boat tends to bounce up and down and bang into oncoming large waves causing a very uncomfortable and unsafe riding condition. Planing hulls generally only work in lightweight high-speed boat designs used over fairly smooth water. Large cargo ships traveling in the open-ocean with large waves do not fit these criteria. By design, these strategies use large water-hull interface, which increases water friction on the vessel.
One strategy to reduce water friction has is to provide an air cavity under the hull, which reduces the hull-to water-contact area. Certain strategies have also been attempted to use air cavities to reduce water displacement such as hover crafts and surface effect ships. However, while thin air cavities have been successfully used to reduce water friction, the use of vessels having air cavities that provide a substantial reduction in water displacement has been met with many challenges, in-part due to the limited acceptable environments for vessel, namely calm and flat sea.
Air cavity hull technology has been in development for more than 50 years. In spite of its history, few implementations have been deemed practical and made into the marine vessel industry. Air cavity hulls add a layer of sophistication and complication as well as additional cost to boat construction. However a properly designed and built air cavity hull boat can add many advantages and cost saving. Innovations to boat hull design can reduce the water displacement.
The term air cavity has the nomenclature of a long shallow flat cavity at the bottom of a boat hull. In sea conditions that present waves, vessels with air cavities that substantially reduce water displacement (rather than merely configured for—friction reduction) often rapidly lose air, e.g. when wave undulation causes a portion of the hull become to airborne. Attempts to overcome this issue have included providing such vessels with retractable walls that give way to an oncoming wave and remain in contact with the water surface. Another strategy has been to provide non-retractable walls, using a step aft of the bow to form a recessed cavity, which tapers thinner to the stern to reduce the cross-sectional area and air volume at the stern to reduce air escape. Although these vessels may reduce instances of total air loss in very small waves, these instances of total air loss are traded for a more gradual loss of air from under the walls that skim across the water surface. Further, these air cavities offer negligible capacity for shock absorption and still experience rapid air loss in larger waves.
U.S. Pat. No. 7,143,710 (Lang et al.) describes a ship hull which includes air cavities, stabilizing fins and canard fins. The air cavities are very short and wide, configured to reduce drag from water friction. Lang et al. do not teach a deep air chamber (e.g. a high aspect ratio chamber) configured to reduce water displacement and provide shock absorption. Further Lang et al. do not teach fins extending from the side walls of an air cavity or air chamber such as inner fins or outer fins. Further, Lang et al. do not teach elongated fins. Further, Lang et al. do not teach a wave piercing bow. Further, Lang et al. do not teach a recirculating air chamber,
U.S. Pat. No. 7,013,826 (Maloney et al.) describers an air chamber hull having retractable bow and stern air cushion seals that raise from the impact of water to maintain an air seal and comprising forward mounted foils. Among features, Maloney et al. do not teach a deep air chamber (e.g. a high aspect ratio chamber), stable fore and aft air chamber walls, elongated fins, fins extending laterally from the sidewalls, neutral fins, a recirculating air chamber, or a wave-piercing bow.
U.S. Pat. No. 6,199,496 (Burg) describes a gas cushion vessel having elongated knife shaped bows that slice into waves having an aft wall that tapers to reduce the cross sectional area at the stern. Among features, Burg does not teach a deep air chamber (e.g. a high aspect ratio chamber), a recirculating air chamber, or fins extending laterally from side walls.
U.S. Pat. No. 7,497,179 (Dize) describes a twin-hull catamaran comprising hydrodynamic lifting V-shaped hulls with mid-span recess that receives air. The recess tapers along the aft wall. Among features, Dize does not teach a deep air chamber (e.g. a high aspect ratio chamber), a recirculating air chamber, a wave-piercing bow, a non-planing hull, or fins extending laterally from side walls.
What is needed in the art is a deep air chamber hull that that provides substantial shock-absorption, depth stabilization, resistance to wave undulation, recirculation of air chamber air, wave-piercing capabilities to traverse large waves, and accommodation for surface propellers.